Instead of just storing the edit history in the message which
triggered the topic edit, we store the edit history in all
the messages that changed. This helps users track the edit history
of a message more reliably.
In 709493cd75 (Feb 2017)
I added code to render_markdown that re-fetched the
sender of the message, to detect whether the message is
a bot.
It's better to just let the ORM fetch this. The
message object should already have sender.
The diff makes it look like we are saving round trips
to the database, which is true in some cases. For
the main message-send codepath, though, we are only
saving a trip to memcached, since the middleware
will have put our sender's user object into the
cache. The test_message_send test calls internally
to check_send_stream_message, so it was actually
hitting the database in render_markdown (prior to
my change).
Before this change we were clearing the cache on
every SQL usage.
The code to do this was added in February 2017
in 6db4879f9c.
Now we clear the cache just one time, but before
the action/request under test.
Tests that want to count queries with a warm
cache now specify keep_cache_warm=True. Those
tests were particularly flawed before this change.
In general, the old code both over-counted and
under-counted queries.
It under-counted SQL usage for requests that were
able to pull some data out of a warm cache before
they did any SQL. Typically this would have bypassed
the initial query to get UserProfile, so you
will see several off-by-one fixes.
The old code over-counted SQL usage to the extent
that it's a rather extreme assumption that during
an action itself, the entries that you put into
the cache will get thrown away. And that's essentially
what the prior code simulated.
Now, it's still bad if an action keeps hitting the
cache for no reason, but it's not as bad as hitting
the database. There doesn't appear to be any evidence
of us doing something silly like fetching the same
data from the cache in a loop, but there are
opportunities to prevent second or third round
trips to the cache for the same object, if we
can re-structure the code so that the same caller
doesn't have two callees get the same data.
Note that for invites, we have some cache hits
that are due to the nature of how we serialize
data to our queue processor--we generally just
serialize ids, and then re-fetch objects when
we pop them off the queue.
All the fields of a stream's recipient object can
be inferred from the Stream, so we just make a local
object. Django will create a Message object without
checking that the child Recipient object has been
saved. If that behavior changes in some upgrade,
we should see some pretty obvious symptom, including
query counts changing.
Tweaked by tabbott to add a longer explanatory comment, and delete a
useless old comment.
Fixes#16284.
Most of the work for this was done when we implemented correct
behavior for guest users, since they treat public streams like private
streams anyway.
The general method involves moving the messages to the new stream with
special care of UserMessage.
We delete UserMessages for subs who are losing access to the message.
For private streams with protected history, we also create UserMessage
elements for users who are not present in the old stream, since that's
important for those users to access the moved messages.
Anders Kaseorg
Aman Agrawal
Steve Howell
Mohit Gupta